Tomo is a wearable, low-cost system using Electrical Impedance Tomography (EIT) to recover the interior impedance geometry of a user’s arm. This is achieved by measuring the cross-sectional impedances between all pairs of eight electrodes resting on a user’s skin. Our approach is sufficiently compact and low-powered that we integrated the technology into a prototype wrist- and arm-band, which can monitor and classify gestures in realtime. We ultimately envision this technique being integrated into future smartwatches, allowing hand gestures and direct touch manipulation to work synergistically to support interactive tasks on small screens.